RFR: JDK-8303349: Simplify link format for generic types in index pages

[Hannes Wallnöfer]

Please review a simple change to simplify the format of links to generic types in various JavaDoc index pages. Previously, these included dedicated links for type parameters and bounds, which seems excessive for use in an index. 

Below are before and after screenshots for `Spliterator.ofPrimitive` (which is admittedly an extreme case) and neighboring index entries. Note that now links to generic types match what we do for executables, where the whole signature is used as link label.

Before:
<img width="804" alt="index-generic-links-1" src="https://user-images.githubusercontent.com/15975/221875901-07899cc7-8822-4e59-8b93-51efb6795a83.png">

After:
<img width="546" alt="index-generic-links-2" src="https://user-images.githubusercontent.com/15975/221875944-b3db5fab-4e11-493b-8499-54bfeccbeb65.png">

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Commit messages:
 - JDK-8303349: Simplify link format for generic types in index pages

Changes: https://git.openjdk.org/jdk/pull/12786/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12786&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303349
  Stats: 64 lines in 6 files changed: 17 ins; 18 del; 29 mod
  Patch: https://git.openjdk.org/jdk/pull/12786.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12786/head:pull/12786

PR: https://git.openjdk.org/jdk/pull/12786